The 13th Symposium on Boundary Layers and Turbulence

### P2A.13

PRESSURE PERTURBATIONS IN LARGE-EDDY SIMULATION OF CANOPY FLOW

Li Wang, Univ. of California, Davis, CA; and R. H. Shaw and E. G. Patton
Perturbations of static pressure in a large-eddy simulation (LES) of air flow through vegetation exhibit a pattern characterized by a combination of high and low pressure. Over an x,z section chosen to pass through an ejection/sweep structure, the high pressure is centered at the intersection of the upper surface of the canopy and of a sloping scalar microfront. The high pressure extends to the ground and is followed by a zone of low pressure within the sweep region. Observations of static pressure at the soil surface in a forest support this picture.

Diagnostic analysis of the calculated pressures indicates that, of the four "components" of the pressure field, the mean-shear and the turbulent-turbulent terms are dominant. Contributions from canopy drag and subgrid-scale motions are each an order of magnitude smaller. Vertical profiles of the standard deviation of each of the pressure components show that mean-shear is the more important term inside the canopy, while the turbulent-turbulent term is the greater contribution above. The mean-shear term peaks at the canopy top because of the peak in the velocity gradient associated with the inflection in the mean velocity profile. In the x,z section, the mean-shear component appears to be vertically aligned, reflecting the vertical alignment in the w-velocity field. On the other hand, the turbulent-turbulent component exhibits a small downstream tilt, presumably characteristic of the turbulent velocity components from which it is constructed and which are aligned by the mean wind shear.

The 13th Symposium on Boundary Layers and Turbulence